package leetcode;

/**
 * Created by lyk on 2017/3/17.
 * Package name: leetcode
 * Porject name: untitled1
 */
public class ReverseLinkedListII {
    public static void main(String[] args) {
        ReverseLinkedListII rllii = new ReverseLinkedListII();
        ListNode ln1 = new ListNode(1);
        ListNode ln2 = new ListNode(1);
        ListNode ln3 = new ListNode(2);
        ListNode ln4 = new ListNode(2);
        ListNode ln5 = new ListNode(2);
        ListNode ln6 = new ListNode(3);
        ListNode ln7 = new ListNode(4);
        ListNode ln8 = new ListNode(5);
        ln1.next = ln2;
        ln2.next = ln3;
        ln3.next = ln4;
        ln4.next = ln5;
        ln5.next = ln6;
        ln6.next = ln7;
        ln7.next = ln8;
        System.out.println(ln1);
        System.out.println(rllii.reverseBetween(ln1,1,7));
    }
    public ListNode reverseBetween(ListNode head, int m, int n) {
        if(head == null) return null;
        ListNode dummy = new ListNode(0); // create a dummy node to mark the head of this list
        dummy.next = head;
        ListNode pre = dummy; // make a pointer pre as a marker for the node before reversing
        for(int i = 0; i<m-1; i++) pre = pre.next;

        ListNode start = pre.next; // a pointer to the beginning of a sub-list that will be reversed
        ListNode then = start.next; // a pointer to a node that will be reversed

        // 1 - 2 -3 - 4 - 5 ; m=2; n =4 ---> pre = 1, start = 2, then = 3
        // dummy-> 1 -> 2 -> 3 -> 4 -> 5

        for(int i=0; i<n-m; i++)
        {
            start.next = then.next;
            then.next = pre.next;
            pre.next = then;
            then = start.next;
        }

        // first reversing : dummy->1 - 3 - 2 - 4 - 5; pre = 1, start = 2, then = 4
        // second reversing: dummy->1 - 4 - 3 - 2 - 5; pre = 1, start = 2, then = 5 (finish)

        return dummy.next;

    }
}
